Revision exercises

Ex.1. Answer the following questions:

1. What is a normal hydrocarbon? 2. In what physical states do alkanes exist? 3. Where are alkanes soluble? 4. What is a non IUPAC name of alkenes? 5. How is an alkene with two double bonds called? 6. How are alkynes prepared? 7. What does hydrogenation of alkynes result in?

Ex.2. Match the words with their definitions:

1. saturated hydrocarbon	a. a chemical reaction that involves the reaction of a compound with halogen and results in the halogen added to the compound;
2. sequence	b. a chemical compound or substance that may speed up or slow down a chemical reaction without itself being changed or consumed at any time during the reaction;
3. isomer	c. the simplest hydrocarbon species which is composed entirely of single bonds;
4. catalyst	d. an ordered collection of elements in which repetitions are allowed;
5. halogenation	e. any chemical reaction that involves the moving of electrons;
6. combustion	f. a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen;
7. oxidation	g. one of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties.

Ex.3. Say whether the following statements are true or false:

1. Alkanes are unsaturated hydrocarbons as they consist of carbon and hydrogen atoms and all bonds are double bonds. 2. The alkanes are sometimes called linear hydrocarbons because the carbon chains are straight. 3. Boiling and melting points of alkanes with the same molecular weights decrease with increasing the number of branches. 4. Most common alkenes found in the chemical laboratory are pungent-smelling liquids. 5. Alkenes may be oxidized to ketones if the carbon in the double bond is attached to two alkyl groups. 6. Alkynes are often referred to as olefins, a non IUPAC name. 7. Alkynes are unsaturated hydrocarbons which contain one or more carbon-hydrogen triple bonds.

Ex.4. Insert the necessary word:

1. The carbon atom in an ... forms four single bonds that are equidistant from each other. 2. The ... of alkanes increases with increasing the number of carbon atoms but is less than that of water. 3. Most reactions of alkanes require specialized ... for breaking the carbon-carbon bonds. 4. Chlorination and hydrogenation are two of the ... reactions that are typical of alkenes. 5. The low-molecular-weight alkenes of importance in the petrochemical industry are ... . 6. The parent ... of alkynes must include the triple bond even if it is not the longest possible carbon chain in the molecule. 7. ... of alkynes produces alkanes and alkenes. (gases, density, hydrogenation, alkane, chain, catalysts, addition)

Unit VII halogens

The halogens are the family of chemical elements that includes fluorine (atomic symbol F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Chlorine was the first halogen to be discovered in 1774, followed by iodine, bromine, fluorine, and astatine was discovered last in 1940.  The halogens make up Group VIIA of the Periodic Table of the elements. Elemental halogens are diatomic molecules. The bonds in these diatomic molecules are non-polar covalent single bonds. Due to their high reactivity, the halogens are never found in nature in native form. Compounds containing more than one kind of halogen are possible. As a general rule, fluorine is the most reactive halogen and astatine is the least reactive. The name "halogen" is derived from the Greek roots hal- ("salt") and -gen ("to form"). Together these words combine to mean "salt former", referencing the fact that halogens form salts when they react with metals. The salinity of the oceans on Earth is due in large part to such halogen salts (halides) as sodium chloride (NaCl) and potassium iodide (KI).

Halogens display physical and chemical properties typical of nonmetals. They have relatively low melting and boiling points that increase steadily down the group. At room temperature, the halogens demonstrate all of the physical states: fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. All of the elements are colored, with the color becoming more intense moving down the group. Fluorine gas is pale yellow, and chlorine gas is a yellowish green. Liquid bromine and its vapors are brownish red. Solid iodine appears as shiny, dark gray crystals, and the vapors are a deep purple. The halogens are poor thermal and electrical conductors in all phases, and as solids they are brittle and crumbly. The halogens have distinctive, unpleasant odors, and are toxic.

The neutral atoms of the halogens possess seven outer electrons, they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups. An additional electron can be added to halogen atoms to form singly charged negative ions. These ions have a closed outer-shell configuration. Electronegativity is a measure of the ability of an atom of one element to remove an electron from an atom of another element. As a group, the halogens are among the most electronegative elements. Fluorine has the highest electronegativity of all the elements. Halogens are so reactive that all the elements except helium and neon have been found to react with at least one of the halogens.